Heretofore, in joining chainstays with a bottom bracket shell on a bicycle frame the bottom bracket shell and chainstays were joined together only by adhesive agents
However, the bicycle frame as above-mentioned has a weakness in that the adhesive strength weakens due to the bicycle frame being under constant stress and strain from every direction. The Japanese Utility Model Application Publication No. Sho 51-54365 is cited as a prior art to solve the problem of the bicycle frame. The prior art comprises a bottom bracket shell defining a pair of cylindrical projecting parts with chainstays around the cylindrical projecting parts bonded thereto, an inner frame between the joining parts of the cylindrical projecting parts and chainstays and a rivet through the inner frame, chainstays and cylindrical projecting parts.
The prior art has the advantage in that the joining construction of the chainstays and bottom bracket shell doesn't loosen when the adhesive agent becomes ineffective.
However, in the joining construction, it is hard to uniformly spread adhesive agent between the cylindrical projecting parts and chainstays.
In addition, it was experimentally discovered that the joining strength of the rivet through the chainstays and cylindrical projecting parts is not enough to compensate for the stress and strain from every direction.